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Citation and License

BMC Cell Biology 2007, 8:49
doi:10.1186/1471-2121-8-49

Published: 20 November 2007

Abstract

Background

Tight junctions are required for epithelial barrier formation and participate in the
regulation of signalling mechanisms that control proliferation and differentiation.
ZO-1 is a tight junction-associated adaptor protein that regulates gene expression,
junction assembly and epithelial morphogenesis. We have previously demonstrated that
the heat shock protein Apg-2 binds ZO-1 and thereby regulates its role in cell proliferation.
Here, we addressed the question whether Apg-2 is also important for junction formation
and epithelial morphogenesis.

Results

We demonstrate that depletion of Apg-2 by RNAi in MDCK cells did not prevent formation
of functional tight junctions. Similar to ZO-1, however, reduced expression of Apg-2
retarded de novo junction assembly if analysed in a Ca-switch model. Formation of functional junctions,
as monitored by measuring transepithelial electrical resistance, and recruitment of
tight and adherens junction markers were retarded. If cultured in three dimensional
extracellular matrix gels, Apg-2 depleted cells, as previously shown for ZO-1 depleted
cells, did not form hollow polarised cysts but poorly organised, irregular structures.

Conclusion

Our data indicate that Apg-2 regulates junction assembly and is required for normal
epithelial morphogenesis in a three-dimensional culture system, suggesting that Apg-2
is an important regulator of epithelial differentiation. As the observed phenotypes
are similar to those previously described for ZO-1 depleted cells and depletion of
Apg-2 retards junctional recruitment of ZO-1, regulation of ZO-1 is likely to be an
important functional role for Apg-2 during epithelial differentiation.